Method of producing a solution of cyanamide from calcium cyanamide



May 29, 1928.

A. N. ERICKSON METHOD OF PRODUCING A SOLUTION 0F CYANAMIDE FROM CALCIUM CYANAMIDE Filed April 20, 1927 pre 6 c400,

*:W I I Quorum Patented May 29 1928.

more sreres Areurorr cn mum N. nmoxson, or :nrmnons'r. rmw YonK, ASSIGNOR 1'0 UNION comma, COMI'ANY, A GORPORATIQN or vmomm.

IIETHOID OB PRODUCING A SOLUTION OF CYANAMIbE FROM CALCIUM GYANAmB.

Application and April 20, 1921' sci-mi No. 155,255.

This invention isa new method of producing a solution of cyanamide from onloium cyanamide and in particular to the production of 'cyanamidc solutions substantially free from (licyandiamidc for use in. the manufacture of urea.

Unless special precautions urc falcon in prepzirin c. uuamirle solutions from calcium cyunami e urge percentages of the cyannmide will be converted into clicyandiatuido. Since ("his latter compound his a harmful effect on plants and can neither be readily converted into urea nor be readily separated therefrom nor from the cynnamide m solution prior to the conversion, by the usual hydrolizing methods. of the cyarmmide conmined therein to urea, it gives rise to an ohjectionable impurit .rin the finzrl urea product. Also, the yie d of urea from u given amount ofcalcinm cyanamirle is, of course, reduced to the extent that; dicyanrlinmide is formed. i

It has been proposed to prepare cyuunmido solutions substantially free from dicynnrliamide by controlling" the alkalinity of the solution during the period in which. the lime content of the calcium cyanamide is being separated thcrcfroni and at the some time sub'ectiug: the solul-ion to moderate .cooli ng.

80 Suc 1 processes for controlling the alkalinity of the solution involve the gradual introduction of calcium oyunnmidc into anaqueous solution while at the some time introducing carbon dioxide under conditions 86 adopted to bring about, the rapid prccipifution of the lime coufontof the calcium cyannmidc. To conduct the opcrntion in n. praclivable manner it. has been found ncccssnry to iutrod'iffie vurious pumps and othcr mov- 40 ing parts into the apparatus and those involve considerable expenditure for repairs and replacement, as well us of power n opera-ting the same.

I have found that the formation of cyan- 4 amide solutions from calcium cyannmicle is not. clepondent upon such close control of the alkalinity of the solution as heretofore has been thought necessary provided certain precautions as to the control of temperature and other factors pro observed. My investigations show that the temperatures relatively low as com cred with those! previously thought fcusi le during the hydration r vcoubexu: being converted into cyunamide substantially free from 'clicya-udiamidc. It thus becomes possible to so conduct the process that :1. whole chargo'or butch of calcium cymuuuiclc may be introduced at once info the required amount of water and tho resulting solution or mixture tractor] with carbon dioxide until all of the limo rind nitrogen are p'rccipitutcd as calcium carbonate and an insoluble lime-nitrogen compound.

The invention has for an object the prop oration of cynnzunirlo solutions substantially free from (iicvamliamidc and to thereby make it possible to produce urea of a. high degree of purity. A further object is to eliminate the more or less complicated pumping and mixing: apparatus heretofore rcquirccl and to reducc operating costs. Other objects will appear from tho followin: description aml drawing, in which lnlim is shown a more or less (liagrmnmu'tic ricw of an apparatus .ndnptetl to he used in carrying out the invention.

In tho drawing 1 is the carhonatingtunk which is provided with a jacket 2 having on inlet ,3 and an outlet 4 for the circulation-of n'cool'mg1 liquid. The jacket ispreferahly open at tho top so that ice may be introrluccd to increase the cflcctivoness'of the cooling liquid. The tank I is provideclu'ith an outlet. 5 loading (on suitable filter 6. t

From the filtcr 6 the solids, consist-lug of the calcium carbonate precipitated in the our honating tank 1 and the insoluble limo-ni trogcn compound, are led to the tank 7 which, similarly to tank 1. is provided with a jacket 8 having an'inlet 9 and an outlet 10 for the. cireulationof a suitable fluid heating medium. If the space between the jacket andthe tank is filled with water, steam may be injected through suitable connectipns, not shown, to raise the temperature of --thc bath to the point Where decomposition of the lime-nitrogen. compound will be iui tiated. When the decomposition of the lime-nitrogen compound is complete the resulting slurry is drawn of? through the out let-11 and passed through the filter 12 to separate the'cyanamide solution from the precipitated calcium carbonate. Carbon dioxide is supplied to the tanks 1 and 7 by means of injectors 13 which comprise a ear; supply pipe 14 leading to a hollow annular member 15 having perforated or porous side walls. A porous material which has been found especially suitable for such side walls is Filtros. An injector 13 is supported above either tank as desired by any suitable means not-shown so that it may he dipped into the solution and withdrawn at will. This flexibility or movability of theinjector 13 gives it marked advantages over injecting .means which form a part of the treating tank, particularly with respect tot-he gr'ea ter ease with which the perforations or pores may be cleaned and opened if they becmue clogged by solids in the solution.

According to 'the present process water in the proportion of about 0.7 gallon for each pound of commercial calcium cyanamide to r be treated is introduced into the tank 1. The whole charge or batch of calcium cyanamide is then added. Carbon dioxide is then passed into the solution until no more free lime is present. This will ordinarily require upwards o'i three hours. The temperature of the solution throughout the hydrating and carbonatinp; step should be maintained below 25 C., and preferably should he maintained between 10 and 20 C. \Vhen the temperature ofthe solution is kept bc low 20 C., the alkalinity remains at about 0.2? normal. lVhile this alkalinity would give rise to considerable dicyandiamide formation at higher temperatures, with temperatures within the range stated substantially no dicyandiamide is formed.

When the carbonation is complete, as indicated by the disappearance oF free lime, the resulting slurry is filtered. Practically all of the nitrogen originally contained in the calcium cyanamide is now contained in the insoluble residue which consists of calcium carbonate and an insoluble lill'l0-Ilit[.0 gen compound, probably calcium cyanamide carbonate. The filtrate, which contains less than 1% of the total nitrogen, may he returned to the carbonatinglank 1 for treating a fresh batch of calcium cyanamide. The filter tzllil' i now il'itroducd into the tank 7, a small amount of water or filtrate from the filteringstep just described is added to the tiller cake, and the resulting sludge is heated at approximately 32 C. until decomposition of the carbonated lime-nitrogen compound is complete. During this heating step carbon dioxide is passed into the sludge in the same manner as described above. About 0.026 gal. of water or filtrate to each pound of calcium cyanamide originally taken is suflicient to insure complete solution of the cyanamide upon decomposition of the insoluble lime-nitrogen compound contained in the sludge. In this connection it is to be noted thatthe carbonated. limenitrogen compound when decomposed yields a considerable volume of water of combination. It is for this reason and to reduce the volume of water present in the final area so lution that the filtering step above described is carried out. In lieu of this filtering step the separation by decantation or a simple thickening process ofa portion of the water contained in the mixed carbonate sludge resulting from the treatment in tank lis not precluded.

When the decomposition of the lime-nitrogen compound is complete the resulting slurry or sludge is filtered The filtrate is a cyanamide solution containing only a. trace of dicyandiamide. This solution may be treated with the usual hydrolizing agents for converting the cyanamide into urea.

I claim:

1. Process of preparing acyanamide solution practicallytree from dicyandiamide' which comprises treating calcium cyanamide with water and carbon dioxide while maintainin; the temperature of the solutionsufficiently low to prevent the formation of substantial amounts of dicyandiamide but at such tcmpera'tm-c as will promote the pre: cipitation of substantially all of the nitrogen as a carbonated lime-nitrogen compound,

separatingat leasta portion of the water From the precipitate, moderately heating the residue. in the presence of carbon dioxide to decompose the lime-nitrogen compound into c \-'anamide and calcium carbonate, and finally separating the cyanamide and carbonate.

2. Process of preparinga cyanamide solution prm-tically free from dicyandiamide which comprises treating calcium cyanamide with water in the presence of carbon dioxide and at a temperature of from 10 to 20 C. 15

until substantially all of the nitrogen is pro ci itated in the form of an insoluble carb nated lime-uitrogeu compound, separating a portion of the water From the precipitate,

heating the residue at about 32 C. while B passing carbon dioxide thereinto to decom pose the lime-nitrogen compound into cyanamide and. calcium carbonate, and finally separating the. cyauamidc and carbonate.

2- Process of preparing a cyanamide so- 1 not lution practically free fromdicyandiamide convert the carbonate into 0 anamide and which comprises forming calcium cyanalnide calcium carbonate, and fins. ly separating carbonate by treating calcium cyanamide the cyanamide solution fr'om the pmcipi- 10 with 'water and carbon dioxide while mainhated calcium carbonate. v v

5 mining the temperature of tha solution be-j In testimony -whereof, I ai'nx my signalow 25 0., heating the carbonate at about ture. v c 391 C. in the presence of carbon dioxide to ALBERT N.-ERICKSON. 

